1. Field of the Invention
The invention relates to a pressure medium operable cylinder/piston unit for the provision of at least one rotary movement.
2. Description of the Prior Art
From the books "Olhydraulik: Grundlagen und Anwendungen" by Prof. E. M. Chaimowitsch, VEB Verlag Technik, Berlin 1958, page 224, and "Olhydraulikfibel" by Werner Dieter, Krausskopf-Verlag, Wiesbaden 1960, page 148, pressure medium operable cylinder/piston units for providing a rotary movement are known, but there is no hint to be found there that both a rotary movement and a longitudinal movement can be provided simultaneously in a cylinder/piston unit.
Although pressure medium operable cylinder/piston units are generally known which perform a longitudinal movement and which also make a simultaneous rotary movement by means of screw threads and the like, such arrangements are not suitable for the separate selective control of a rotary movement and a longitudinal movement.
Separately controllable rotary and longitudinal movements are extremely advantageous for use in hydraulically operated gear shifting mechanisms in change-speed gearboxes. The pressure medium operable cylinder/piston units previously used in this field have made these two different movements available, but always by means of separate units.
From German Patent 30 17 464, a pressure medium operable gear shifting aid for a manual change-speed gearbox is known, wherein a gearshift rod can be operated by a rotary piston to engage the gear speeds. However, to select different shifting arms of various gearshift rods, the striker is arranged axially displaceably on the gearshift rod and must be axially displaced by the driver personally. Thus, the gear shifting aid only makes hydraulic support available for the engagement of the gear speeds.
From German published Patent Application 37 01 690, a servo drive for the operation of a gearshift rod of a change-speed gearbox of a motor vehicle is known, which makes available both a rotary and a longitudinal movement of gearshift rod by means of alternately pressurisable pressure chambers, but here the rotary movement is obtained through a kind of crank mechanism and the pressure chambers are in the form of membrane pressure chambers.
It is an object of the invention to provide a pressure medium operable cylinder/piston unit, which can in particular be used for the automatic shifting of a change-speed gearbox of a motor vehicle, and which makes available both a rotary selection movement required for the preselection of the gate arm for the gear speed and also a longitudinal engaging movement required for the engagement of the gear speed.